On June 25, 1950, North Korean forces crossed the 38th parallel in a coordinated invasion of South Korea. The United Nations authorized a multinational response led by the United States; China intervened in October 1950 when UN forces approached the Yalu River. Three years of fighting produced approximately one million military deaths and up to three million civilian casualties. The July 1953 armistice established a 4-kilometer Demilitarized Zone but no peace treaty, leaving the two Koreas technically at war.